The present invention relates to apparatus disposed at a first location and activated from a second location over a link between the first location and the second location. The apparatus to which the present invention relates can include switch means whose switching state is changed when the apparatus is activated over the link. The switch means can be used to disconnect equipment from and/or connect equipment to the link at the first location. More particularly, the present invention relates to apparatus disposed at a subscriber's facility activated from a communication company office over a line linking the communication company office and the subscriber so as to disconnect and/or connect the line and the subscriber's equipment.
Apparatus connected to a telephone line at a subscriber's facility for the purpose of disconnecting subscriber equipment from the line and/or connecting further apparatus to the line in response to a signal sent over the telephone line from a telephone company office are known and are referred to as remote isolation or disconnect devices, line testers, and other terms. The signal sent from the telephone company office can be DC, pulsed or AC, or combinations thereof. Some apparatus will disconnect subscriber equipment from the line in response to the signal sent over the line and then automatically reconnect the equipment to the line after the elapse of a controlled time period, which can be measured, for example, from the time of application or removal of the signal, or from the time of disconnecting the equipment. Some apparatus will maintain the subscriber's equipment disconnected until another signal is sent over the telephone line from the telephone company office to reconnect the subscriber's equipment. During the time that the subscriber's equipment is disconnected from the telephone line by apparatus of the type described above, the telephone line up to the subscriber's facility can be tested remotely from a telephone company office. Apparatus of the type described above can terminate the telephone line at the subscriber's facility with a specified impedance including a short or open circuit to provide a known passive signature in place of the subscriber's equipment. It is also known to couple active circuits such as tone generators to the telephone line in place of the subscriber's equipment.
Many of the known apparatus of the type described above which temporarily disconnect and automatically reconnect the subscriber's equipment within a controlled time period include an energy storage device such as a capacitor which is caused to charge or discharge by or in response to a signal sent from the telephone company office. U.S. Pat. Nos. 3,725,613 (Allen et al.), 3,773,986 (Tremblay), 4,054,759 (McGrath et al.), 4,143,250 (Simokat) and 4,169,220 (Fields) all disclose remotely activated apparatus which includes a capacitor charged and/or discharged by or in response to a signal sent from a telephone company office. U.S. Pat. No. 3,867,588 (Pickens et al.) discloses remotely activated apparatus which includes a battery charged by a signal sent from a telephone company office. The charging or discharging capacitor (or battery) causes a switch to change its switching state and disconnect the subscriber's equipment. Thereafter, upon the discharging or charging of the capacitor (or battery), which occurs automatically within some controlled time period after the initial application or subsequent removal of the telephone company activating signal, the switch reverts to its original state to reconnect the subscriber's equipment.
The telephone company coin collection (+130v DC) or coin return (-130 v DC) voltage can be used as the activating signal, as known, as well as other telephone company signals which may be generated at a telephone company test desk.
The capacitor (or battery) can be charged from the telephone signal (as, for example, in the Fields '220 and Pickens et al. '588 patents) or from a power source typically provided as part of the apparatus disposed at the subscriber's facility (as, for example, in the Tremblay '986 patent). Heretofore, in remotely-activated apparatus which utilized the energy from a telephone company signal to charge a capacitor, the time that the telephone company signal had to be applied to the apparatus in order to charge the capacitor so that the switch would be maintained in a switched state for a given time could not be accurately determined because of variations in the telephone company signal itself, telephone line conditions and circuit components in the apparatus. In addition, because of variations in the telephone company signal, telephone line conditions and circuit components, the time that the switch would be maintained in the switched state also could not be accurately determined.
While a prior art system which utilized a battery or other power source for charging the capacitor might provide some improvement in determining switching time, batteries have the disadvantage of limited life and output variations with age and environmental conditions, and the use of batteries or other power sources adds to the expense of the apparatus, particularly batteries which have to be replaced periodically if reliability is to be assured.
In the Pickens et al. '588 patent, a battery is charged by a telephone company signal for a predetermined time. Upon removal of the telephone company signal, the battery discharges through a relay coil which controls a switch coupling a telephone line to a subscriber. While it might be possible to charge the battery to a generally known potential by controlling the length of time that the telephone company signal is applied, the magnitude of the telephone company signal which the battery receives is subject to changes caused by conditions on the line linking the telephone company office and the subscriber. Thus, the battery may not be charged by a precisely known voltage and the voltage which charges the battery may not be the same from activation to activation. Therefore, the discharge time may not be precisely determined and may not be repeatable from activation to activation. As mentioned above, the inclusion of a battery in a remotely activated apparatus adds to the expense of the tester and can reduce the reliability of the tester.
In U.S. Pat. No. 3,852,537 (Vincent), two capacitors which are discharged through different relay coils to connect and disconnect subscriber equipment from a telephone line are charged by a signal regulated by a zener diode. However, the charging signal is the line voltage normally present on the telephone line rather than a selectively applied signal so that charging time of the capacitors is as a general matter not a concern.
Some known apparatus of the type described above which disconnect the subscriber's equipment in response to a first signal sent over the telephone line and maintain the equipment disconnected until a second signal is sent over the telephone line include a relay or other device which is latched in response to the first signal and unlatched in response to the second signal. For example, in U.S. Pat. Nos. 3,919,487 (Gabrielson), 4,041,255 (Cambridge et al.) and 4,126,771 (Proctor et al.), and the Vincent '537 patent, a latching relay is utilized as the latching device and in U.S. Pat. No. 4,258,236 (Conklin et al.) a latching circuit is used as the latching device. However, apparatus disclosed in these patents which disconnected or reconnected the subscriber's equipment in response to a particular signal, also had the drawback that the precise time necessary to apply the particular signal to effect a disconnect or reconnect could not accurately be determined and/or was not accurately repeatable.
The present invention provides improved remotely-activated apparatus which does not suffer from the aforementioned drawbacks.